High-resolution Fourier transform infrared spectrum of the [formula omitted] band of formamide-d1 (DCONH2)

Abstract

The high-resolution rovibrational spectrum of the ν6 band of formamide-d1 (DCONH2) was recorded using the Fourier transform infrared (FTIR) spectrometer at the Australian Synchrotron with an unapodized resolution of 0.00142 cm−1 in the mid-infrared region of 910–990 cm−1 region. From the rovibrational analysis of this A-type band, the v6 = 1 state rovibrational constants up to one sextic term were derived for the first time from a total of 1450 infrared transitions. These transitions were fitted using the Watson's A-reduced Hamiltonian in the Ir representation with a root-mean-square (rms) deviation of 0.00078 cm−1. The center of the ν6 band of DCONH2 was accurately determined to be 954.857070(41) cm−1. This v6 = 1 state was found to be perturbed by the nearby (v10=1,v12 = 1) state, just around 16 cm−1 higher. Two c-Coriolis parameters were obtained from the perturbation analysis of the interaction between the rotational energy levels of the v6 = 1 and (v10=1,v12 = 1) states. Additionally, the center of the ν10+ν12 band was found at 970.671(41) cm−1 and rotational constant C was fitted accurately. Ground state rotational constants and centrifugal distortion constants up to two sextic terms were obtained by fitting of 1432 ground state combination differences (GSCDs) derived from the infrared (IR) transitions of both the ν6 band of the present work and ν12 band of previous work of DCONH2, together with 6 previously reported microwave frequencies. The root-mean-square (rms) deviation value of this fit was 0.000183 cm−1. The ground state constants in this study provide a better representation for the DCONH2 isotopologue as the values were derived from a larger pool of GSCDs. In addition, ground state rovibrational constants up to five quartic terms and rotational constants of the v6 = 1 state were computed from theoretical anharmonic calculations at two different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results.